By Rodrigo Viga Gaier

RIO DE JANEIRO, May 26 (Reuters) - Brazil's Petrobras PETR4.SA wants to review Braskem's BRKM5.SA shareholders agreement for possible changes to allow it more say in the petrochemical firm's decisions, three sources close to the matter at the state-run oil firm told Reuters.

Petrobras has a 47% voting stake in the petrochemical company but has appointed four of 11 board members and one director out of seven, numbers it considers small, according to the sources.

Last week, Braskem's majority stakeholder Novonor received a non-binding proposal from a fund owned by businessman Nelson Tanure to acquire control of the largest petrochemical company in Latin America.

Novonor has been trying to sell its stake in Braskem for years, but has repeatedly failed to reach a deal.

Petrobras' objective would be to obtain a new agreement akin to the one it got in Eletrobras, where it increased the number of seats it appoints to the board of the former state-run firm, expanding its influence.

In the event of a sale, Petrobras has preference rights to buy Novonor's stake, but the sources said Petrobras has no interest in increasing its voting share.

Petrobras wants instead to have a more active voice in the management and operations of the petrochemical company, regardless of who is the controlling partner, said the sources.

On Monday, Petrobras CEO Magda Chambriard said Tanure's proposal is a move in the right direction.

"Whatever solution that works out will have Petrobras' support," said Chambriard.

Braskem and Petrobras did not immediately respond to requests for comment.

(Reporting by Rodrigo Viga Gaier, translation by Fabio Teixeira; Editing by Rod Nickel)

((Fabio.Teixeira@thomsonreuters.com; +55 21 99603-4782;))